Background/Purpose:

Gout is typically characterized as an acute monoarthritis involving the joints of the foot. However, polyarticular involvement develops, especially in advanced disease. Patterns of involvement of monosodium urate (MSU) crystal deposition such as symmetry and clustering in patients with gout has never been described. The aim of this study was to evaluate patterns of MSU deposition using dual-energy CT (DECT) among gout patients on urate-lowering therapy (ULT).

Methods:

Using standardized acquisition protocols, DECT scans of the feet/ankles, knees, and hands/wrists were prospectively obtained in 153 patients with a known diagnosis of gout (all meeting 1977 ARA gout classification criteria) and on allopurinol at a dose of at least 300mg daily for at least 3 months. MSU deposition was evaluated by 2 DECT radiologists at 12 sub-sites in the feet/ankles, 4 sub-sites in the knees, and 15 sub-sites in the hands/wrists. We calculated the number of subjects who would have 0, 1, 2, 3, 4, or 5+ joints with MSU deposition, assuming that its presence in different joints in a subject is independent. Clustering of MSU deposition in the 3 regions was assessed using a χ²-test. We then evaluated the patterns of MSU deposition at different joints with generalized estimating equations while adjusting for age, sex, and race.

Results:

Our analysis included 153 patients (92% male) with gout (mean disease duration, 15 years) on allopurinol (mean duration of therapy, 5 years; mean daily dose, 333mg). MSU deposition was observed in a clustered manner at multiple joints of the hands/wrists, feet/ankles, and knees more frequently than would be expected by chance (p<0.001 for all 3 regions). Presence of MSU deposition at a given joint was strongly associated with MSU deposition at the same joint of the opposite extremity (i.e., symmetric involvement), followed by other joints in the same ray of the hand or foot (i.e., multiple joints of one digit), followed by other joints in the same row of the hand or foot (i.e., same joint across multiple digits).

Conclusion:

MSU deposition often affects multiple joints of the feet/ankles, knees, and hands/wrists in a clustered manner. MSU deposition tends to occur in a highly symmetric pattern in all three regions evaluated. In the hands and feet, MSU deposition is more likely to cluster by ray (i.e., multiple joints of one digit) than by row (i.e., same joint across multiple digits). These findings may shed light on pathophysiologic factors that lead to MSU deposition and may inform clinicians’ decisions to obtain bilateral vs unilateral imaging of a target joint.

Table 1 – Pattern of MSU Deposition in Treated Patients with Gout

*Adjusted for other joints, age, sex and race.